ER Practice Q's - Week 2 - Male Reproductive System
ANSWER: B: Primordial germ cells Rationale: Teratomas are the most common testicular tumor in the age group between 4 and 12 years. They are derived from primordial germ cells that have become activated to initiate embryonic development. Benign teratomas in the prepubertal testes are composed of mature somatic tissues representing all three embryonic germ layers (ectoderm, mesoderm, and endoderm). Spermatogonia (choice E) give rise to monomorphic germ cell tumors, termed seminomas. None of the other testicular cells gives rise to male germ cell tumors.
A 10-year-old boy is brought to the physician because his parents noticed a mass on his left testicle. Biopsy of the mass reveals a haphazard arrangement of differentiated tissues, including squamous epithelium, glandular epithelium, and cartilage. This benign tumor most likely originated from which of the following cells of the male reproductive system? (A) Leydig cells (B) Primordial germ cells (C) Sertoli cells (D) Spermatocytes (E) Spermatogonia
ANSWER: B: Cryptorchidism Rationale: Cryptorchidism is a congenital abnormality in which one or both testes are not found in their normal position in the scrotum. It is the most common urologic condition requiring surgical treatment in infants. In 5% of male infants born at term and 30% of those born prematurely, the testes are not located in the scrotum. In the large majority of these infants, the testis will descend into the scrotum during the first year of life. The descent of the testis may be arrested at any point from the abdominal cavity to the upper scrotum. Anorchia (choice A) refers to congenital absence of testes. Inguinal hernias (choice C) represent protrusion of a portion of the small intestine through the inguinal canal. Macroorchidism (choice D) is a pathologic finding in adult patients with fragile X syndrome.
A 2-month-old boy is brought to the physician because his parents cannot find one of his testicles. Physical examination confirms the parents' observation. Which of the following is the most likely medical diagnosis? (A) Anorchia (B) Cryptorchidism (C) Inguinal hernia (D) Macroorchidism (E) Hermaphrodite
ANSWER: C: Leydig cells Rationale: The circle encloses a cluster of polygonal cells in the connective tissue between adjacent seminiferous tubules. These interstitial cells of Leydig express cell surface receptors for LH and secrete testosterone. Leydig cells are the major source of androgens in males. Granulosa cells (choice B) nourish developing oocytes in the ovaries and secrete estrogen. None of the other cells are found within the testes.
A 23-year-old man presents with a solid testicular mass that is removed surgically (orchiectomy). In addition to neoplastic cells, the surgical specimen shows a margin of normal testicular tissue (shown in the image). Identify the cluster of cells with rounded nuclei within the circle. (A) Follicular cells (B) Granulosa cells (C) Leydig cells (D) Oxyphil cells (E) Parafollicular cells
ANSWER: E: Sertoli cells Rationale: The SRY gene on the Y chromosome encodes testis-determining factor (TDF), which acts as a master switch to regulate the expression of several genes involved in the development of the male reproductive system (e.g., SOX-9, AMH, and SF-1). Female reproductive organs develop in the absence of SRY gene expression. Under the influence of TDF, Sertoli cells differentiate in the primitive sex cords and secrete müllerian-inhibiting factor (MIF). This large glycoprotein hormone suppresses the growth of the paramesonephric ducts that give rise to the uterus and the uterine tubes. Sertoli cells secrete MIF until the time of puberty, after which serum levels of MIF decline. Sertoli cells are the major cell population in the seminiferous tubules during embryonic and fetal development.
A 30-year-old pregnant woman asks for information regarding gender determination in her unborn child. You explain that the SRY gene on the Y chromosome encodes a protein that determines male gonadal sex and that female reproductive organs are inhibited from developing in male embryos by müllerian-inhibiting factor (MIF). Which of the following cells in the embryo and fetus secrete this glycoprotein hormone? (A) Follicular cells (B) Leydig cells (C) Mesothelial cells (D) Primordial germ cells (E) Sertoli cells
ANSWER: C: Infertility Rationale: Blood and lymph vessels in the testes are located outside the seminiferous tubules in the interstitial tissue. The delivery of nutrients and oxygen to spermatogenic cells requires diffusion through peritubular fascia (tunica propria). Age-related thickening of the tunica propria leads to chronic hypoxia and tissue atrophy and reduced rates of spermatogenesis. Thickening of the tunica propria earlier in life would be associated with male infertility. Hydrocele (choice A) refers to a collection of serous fluid in the scrotal sac between the two layers of the tunica vaginalis. It is the most common cause of scrotal swelling in infants and is often associated with inguinal hernia. Infection (choice B) and necrosis (choice D) are unlikely consequences of thickening of the tunica propria. Varicocele (choice E) represents a local dilation of testicular veins and presents as nodularity on the lateral side of the scrotum.
A 55-year-old man with testicular lymphoma has his testicle removed (orchiectomy). In addition to the solid tumor, microscopic examination of the surgical specimen reveals significant thickening of peritubular tissue (tunica propria) of the seminiferous tubules. Which of the following is a complication of this incidental histopathologic finding? (A) Hydrocele (B) Infection (C) Infertility (D) Necrosis (E) Varicocele
ANSWER: B: Corpora amylacea Rationale: The arrow on this image identifies secretory material of the prostate gland that has precipitated within the lumen of an alveolus. These calcified proteinaceous concretions are termed corpora amylacea (amyloid bodies). The structure revealed in this image lacks evidence of cell nuclei and is, therefore, unlikely to represent a cluster of malignant cells (choice A) or amultinucleated giant cell (choice D). Glassy membranes (choice C) represent the basement membranes of atretic ovarian follicles. Residual bodies (choice E) are large vesicles that contain shed organelles and cytoplasm of spermatids undergoing spermiogenesis.
A prostate needle biopsy is obtained from a 70-year-old man with elevated serum levels of prostate-specific antigen (PSA, 10.5 ng/mL). The specimen is embedded in paraffin, stained with H&E, and examined in the pathology department (shown in the image). Identify the structure indicated by the arrow. (A) Cluster of malignant cells (B) Corpora amylacea (C) Glassy membrane (D) Multinucleated giant cell (E) Residual body
ANSWER: D: Tunica albuginea Rationale: The seminiferous tubules are surrounded and protected by a dense, connective tissue capsule that is referred to as the tunica albuginea (white coat). The posterior wall of this tunic is thickened to form the mediastinum of the testis (shown in the image). Connective tissue septa leave the mediastinum and penetrate the testis, dividing it into approximately 250 lobules. Each lobule contains one to four seminiferous tubules, surrounded by interstitial connective tissue. Spermatic fascia (choice B) surrounds the spermatic cord; it arises during development as a continuation of transversalis fascia of the abdominal wall (choice C). Tunica vaginalis (choice E) is a serous sac derived from parietal peritoneum during descent of the fetal testes into the scrotum. None of the other choices contribute to the mediastinum of the testis.
A section through the mediastinum of the testis is examined in the pathology department (shown in the image). Identify the structure indicated by the asterisk. (A) Scrotal ligament (B) Spermatic fascia (C) Transversalis fascia (D) Tunica albuginea (E) Tunica vaginalis
ANSWER: A: Arrow 1 Rationale: This image shows a cross-section through a seminiferous tubule. Sertoli cells are tall, columnar, epithelial cells with basal membranes attached to the tunica propria and apical membranes facing the lumen of the tubule. The lateral and apical membranes of Sertoli cells envelop and nourish 30 to 50 germ cells at various stages of spermatogenesis and spermiogenesis. Sertoli cell nuclei are distinctly oval or triangular in shape. These supporting (sustentacular) cells have receptors for FSH and testosterone and serve as the principal regulator of spermatogenesis. Sertoli cells secrete many proteins, including androgen-binding protein (ABP). ABP concentrates testosterone and dihydrotestosterone within the seminiferous tubules and excurrent genital ducts. Sertoli cells also secrete inhibin—a glycoprotein hormone that inhibits pituitary secretion of FSH. None of the other cells exhibit the distinctive nuclear morphology of Sertoli cells. These cells include early spermatids (arrow 2), late spermatids (arrow 3), primary spermatocytes (arrow 4), and spermatogonia (arrow 5).
A thin (1.5 μm) plastic section of an adult testis is examined at high magnification in the histology laboratory (shown in the image). Which of the following numbered arrows identifies the nucleus of a Sertoli cell? (A) Arrow 1 (B) Arrow 2 (C) Arrow 3 (D) Arrow 4 (E) Arrow 5
ANSWER: C: Arrow 3 Rationale: Spermatids are post meiotic cells with a haploid (23n) karyotype. Spermatids undergo extensive nuclear and cytoplasmic remodeling as they differentiate into sperm. This process is termed spermiogenesis. The release of sperm into the lumen of the seminiferous tubule is termed spermiation. Early and late spermatids are distinguished by their small size, condensed chromatin, and proximity to the lumen of the seminiferous tubule. The nuclear morphology of early and late spermatids is notably different. Late spermatids have highly condensed chromatin, in which nuclear histones are replaced by small peptides termed protamines. Once late spermatids are released into the lumen of the seminiferous tubule, they are appropriately referred to as spermatozoa. None of the other cells exhibit the distinctive nuclear morphology of late spermatids.
A thin (1.5 μm) plastic section of an adult testis is examined by light microscopy in the histology laboratory (shown in the image). Which of the following numbered arrows identifies the nucleus of a late spermatid? (A) Arrow 1 (B) Arrow 2 (C) Arrow 3 (D) Arrow 4 (E) Arrow 5
ANSWER: A: Arrow 1 Rationale: The image shows a cross-section through a seminiferous tubule. The seminiferous epithelium is complex and stratified. Examination of the image reveals germ cells at variousstages of spermatogenesis, including primary spermatocytes (arrow 1), early spermatids (arrow 2), and spermatogonia (arrow 5). The image also reveals Sertoli cells (arrow 3) and myoid cells of the tunica propria (arrow 4). Primary spermatocytes are arrested in prophase of meiosis I. Their chromosomes are duplicated and highly condensed, making primary spermatocytes easy to recognize by light microscopy. Homologous chromosomes in primary spermatocytes are paired. These tetrads undergo homologous recombination (crossing over) to enhance genetic diversity. None of the other testicular cells exhibit the distinctive nuclear morphology of primary spermatocytes.
A thin (1.5 μm) plastic section of an adult testis is examined by light microscopy in the histology laboratory (shown in the image). Which of the following numbered arrows identifies the nucleus of a primary spermatocyte? (A) Arrow 1 (B) Arrow 2 (C) Arrow 3 (D) Arrow 4 (E) Arrow 5
ANSWER: E: Sertoli cells Rationale: Sertoli cells are both exocrine and endocrine cells. For example, Sertoli cells release inhibin, a polypeptide hormone that provides negative feedback inhibition of FSH secretion from the pituitary gland. Sertoli cells also secrete fluid and proteins into the lumens of the seminiferous tubules. These proteins include plasminogen activator, transferrin (iron transport protein), and androgen-binding protein (ABP). ABP has high affinity for testosterone and dihydrotestosterone. ABP serves to maintain a high concentration of these steroid hormones within the seminiferous tubules and the excurrent duct system (epididymis and vas deferens), as well as within the male accessory glands (seminal vesicles and prostate gland). None of the other cells secrete androgen-binding protein.
Androgen-binding protein (ABP) helps maintain a high concentration of testosterone within excurrent ducts and accessory glands of the male reproductive system. Which of the following cells in the adult testis secrete this important steroid-binding protein? (A) Early and late spermatids (B) Leydig cells (C) Primary spermatocytes (D) Principal cells of the prostate (E) Sertoli cells
ANSWER: E: Principal piece Rationale: The principal piece of the sperm flagellum is approximately 40-μm long. It is composed of microtubules and associated molecular motor proteins (e.g., dynein). Sliding of these microtubules generates sperm motility (flagellar beat). In addition to the axoneme (9 + 2 arrangement of microtubules), the principal piece of the sperm flagellum contains outer dense fibers and a fibrous sheath. These structural proteins surround the axoneme and play an essential role in sperm motility. They influence (1) the degree of flexion of the flagellum, (2) the plane of motion of the flagellum, and (3) the curvilinear shape of the flagellar beat. Mutations in the genes for the outer dense fiber and fibrous sheath proteins lead to abnormal sperm morphology and infertility. None of the other choices describe the location of the fibrouss heath in human sperm.
As part of your research project, you create an IgM monoclonal antibody directed to the sperm fibrouss heath protein. Indirect immunofluorescence assays using fluorescein-conjugated anti-mouse IgM demonstrate that your monoclonal antibody binds to which region of the human spermatozoan? (A) Acrosome (B) End piece (C) Middle piece (D) Neck (E) Principal piece
ANSWER: C: Myoid cells Rationale: The tunica propria of the seminiferous epithelium is composed of multiple layers of collagen fibrils and myoid cells. These contractile cells create peristaltic waves that propel sperm and fluid through the seminiferous tubules toward the excurrent genital duct system. In addition to their contractile property, peritubular myoid cells play a role in collagen biosynthesis. The nuclei of fibroblasts (choice B) appear nearly identical to those of myoid cells; however, myoid cells are much more abundant than fibroblasts in the tunica propria. Endothelial cells (choice A), fibroblasts (choice B), and plasma cells (choice D) are present within interstitial tissue of the testes. Spermatogonial stem cells are small, nondescript cells present within the basal compartment of the seminiferous epithelium.
For the surgical specimen that shows a margin of normal testicular tissue, identify the peritubular cells with flattened nuclei indicated by the arrows. (A) Endothelial cells (B) Fibroblasts (C) Myoid cells (D) Plasma cells (E) Spermatogonial stem cells
ANSWER: A: Mesonephric duct Rationale: The genital and urinary systems are structurally and functionally related in both males and females. They develop in close proximity within the intermediate mesenchyme of the urogenital ridge. The excurrent ducts of the male reproductive system (i.e., ductuli efferentes, epididymis, and vas deferens) are all derived from mesonephric tubules and ducts that contribute to the interim kidneys that produce urine during weeks 4 to 8 of development. Metanephric blastema (choice B) is a mass of undifferentiated nephrogenic mesenchyme that forms the nephrons within the permanent kidneys. Paramesonephric duct (choice C) forms the uterus and uterine tubes in females. Ureteric diverticulum (choice D) is a branch of the mesonephric duct that gives rise to the ureter, renal pelves, major and minor calyces, and collecting tubules/ducts of the permanent kidney. Urogenital sinus (choice E) forms the bladder, as well as various male and female reproductive organs.
The excurrent genital duct was derived from which of the following structures during embryonic development? (A) Mesonephric duct (B) Metanephric blastema (C) Paramesonephric duct (D) Ureteric diverticulum (E) Urogenital sinus
ANSWER: B: Reserve stem cells Rationale: The arrows on this image identify basal stem cells. These nondescript cells, with rounded nuclei, undergo terminal differentiation to repopulate the surface epithelium. A thin layer of smooth muscle surrounds the ducts of the epididymis (note peritubular flat nuclei, shown in the image). Peristaltic contractions of these cells help to move sperm and fluid toward the vas deferens. This image also provides an excellent view of apical membrane stereocilia and sperm within the lumen of the tubule. Secretion of sperm maturation factors (choice C) is a reasonable choice for this question, but evidence to support this hypothesis is lacking. None of the other cellular functions characterize basal epithelial cells in the epididymis.
The male reproductive organ is examined at high magnification (shown in the image). What is the principal function of the cells identified by arrows in this pseudostratified epithelium? (A) Fluid uptake (B) Reserve stem cells (C) Secretion of sperm maturation factors (D) Steroid hormone secretion (E) Testosterone binding and uptake
ANSWER: D: Nuclear transcription factor Rationale: Testis- determining factor (TDF) is a transcription factor that binds to a unique sequence of DNA. Binding alters the helical structure of DNA, forming a loop that permits other transcription factors to bind to DNA and modulate gene expression. None of the other choices describe TDF or its mechanism of action.
Regarding the research topic, testis-determining factor (TDF) belongs to which of the following families of proteins? (A) Cytoplasmic adenylate cyclase (B) G protein-coupled receptor (C) Membrane tyrosine kinase (D) Nuclear transcription factor (E) Paracrine signaling hormone
ANSWER: E: Vas deferens Rationale: The ductus (vas) deferens passes along the posterior wall of the testis and through the inguinal canal, before entering the abdomen to join the duct of the seminal vesicle and enter the prostate gland. Once the vas deferens enters the prostate gland, it is referred to as the ejaculatory duct. Unlike the other male reproductive organs listed, the vas deferens is characterized by the presence of a thick muscular wall. Close examination of this autopsy specimen reveals three distinct layers of smooth muscle fibers: inner longitudinal, middle circular, and outer longitudinal. This muscular wall contracts to expel sperm during ejaculation. All of the male reproductive organs listed possess smooth muscle external to the basal lamina of the lining epithelium; however, the muscle wall of the vas deferens is significantly thicker than any of the other choices.
Various male reproductive organs are examined at autopsy. Identify the organ shown in the image. (A) Epididymis (B) Prostate gland (C) Seminal vesicle (D) Testis (E) Vas deferens
ANSWER: D: Intracellular lipid droplets Rationale: Like other steroid-secreting endocrine cells, Leydig cells are characterized by the presence of innumerable intracellular lipid droplets. As a result, Leydig cells appear to have a foamy cytoplasm when examined by light microscopy. Cells with a similar, vacuolated appearance are observed in the adrenal cortex (foam cells). Membrane-bound, dense core secretory granules (choice B) are a characteristic feature of neuroendocrine cells (e.g., chromaffin cells of the adrenal medulla). None of the other cellular organelles are ultra-structural features of Leydig cells.
When examined by electron microscopy, which of the following cytologic features best characterizes interstitial cells of Leydig? (A) Apical membrane microvilli (B) Dense core secretory granules (C) Glycogen vacuoles (D) Intracellular lipid droplets (E) Segmented nuclei
ANSWER: A: Intermediate Rationale: Mesoderm is generated through complex changes in cell adhesion and migration during gastrulation. These stem cells are organized on either side of the neural tube as blocks of tissue, referred to as paraxial, intermediate, and lateral plate mesoderm. Intermediate mesoderm gives rise to the kidneys and the gonads. The urinary and genital systems are closely associated—both anatomically and functionally. For example, the tubules and ducts of the embryonic urinary system (meso-nephros) are retained in male embryos as the excurrent genital ducts. Lateral plate mesoderm (choices B and C) gives rise to the appendicular skeleton, as well as serous membranes that line body cavities and smooth muscle associated with the gut tube. Paraxial mesoderm (choice D) condenses to form somites (choice E), which give rise to the axial skeleton, skeletal (voluntary) muscle, and dermis.
During your lecture, you discuss the origin of the testes in the embryo. The urinary and genital systems both develop from which of the following types of early mesoderm? (A) Intermediate (B) Lateral plate somatic (C) Lateral plate splanchnic (D) Paraxial (E) Somitic
ANSWER: C: Centrosome Rationale: The neck of the spermatozoan contains a pair of centrioles that organize the 9 + 2 arrangement of microtubules in the sperm flagellum during spermiogenesis. This microtubule-organizing center is referred to as the sperm centrosome. Acrosome (choice A) is a membrane-bound vesicle in the head region of the spermatozoan. Centromere (choice B) is a region of chromosomal DNA that organizes and links sister chromatids together and organizes the kineto-chore protein complex (choice E) during cell division. Karyosome (choice D) is a discrete region of heterochromatin that may be visible by electron microscopy in the nuclei of some cells.
Electron microscopy also reveals sperm-associated microtubules and outer dense (coarse) fibers. Which of the following organelles initiates the assembly of microtubules in the axoneme of the sperm flagellum during spermiogenesis? (A) Acrosome (B) Centromere (C) Centrosome (D) Karyosome (E) Kinetochore
ANSWER: C: Glans penis Rationale: The corpus spongiosum surrounds the spongy urethra along the ventral surface of the penis. The corpus spongiosum expands distally to form the glans penis. The cylindrical erectile masses of the penis contain cavernous sinuses separated by trabeculae that are composed of interstitial connective tissue, as well as blood/lymphatic vessels and smooth muscle fibers. The overlaying skin of the penis is thin and loose. Blood is supplied to the penis by the dorsal and deep arteries of the penis—branches from the internal pudendal artery. The penis is innervated by both somatic and autonomic nerve fibers. None of the other anatomic structures are derived from the corpus spongiosum of the penis.
For the specimen shown in the image, the erectile tissue that surrounds the spongy urethra gives rise to which of the following structures of the penis? (A) Central vein (B) Deep dorsal vein (C) Glans penis (D) Prepuce (foreskin) (E) Urethral glands
ANSWER: B: Pseudostratified epithelium surrounded by layer of smooth muscle Rationale: The seminal vesicles consist of a secretory epithelium (nonciliated columnar cells), a thin layer of smooth muscle, and afibrous coat. Parallel cords of polygonal cells (choice A) are seen in the adrenal cortex. Secretory epithelial cells lining follicles (choice C) are seen in the thyroid gland. Simple squamous cells lining open vascular spaces (choice D) are seen in sinusoid capillaries throughout the body. Solid clusters of epithelial cells (choice E) describe nests of endocrine cells that are found in many locations, including the pituitary and parathyroid glands.
Which of the following best characterizes the histology of the male accessory gland, the Seminal vesicle? (A) Parallel cords of polygonal epithelial cells and sinusoidal capillaries (B) Pseudostratified epithelium surrounded by a layer of smooth muscle (C) Secretory epithelial cells lining follicles filled with glycoprotein (D) Simple squamous epithelial cells lining open vascular spaces (E) Small, solid clusters of epithelial cells interlaced with fenestrated capillaries
ANSWER: D: No clinical significance Rationale: Corpora amylacea are commonly observed in the prostate glands of elderly men. Their number increases with age. This incidental histopathologic finding does not seemto carry clinical significance. None of the other mechanisms of disease are linked to the formation of corpora amylacea in the prostate glands of elderly men.
Which of the following best describes the clinical significance of the structure identified as Corpora amylacea? (A) Chronic inflammation (B) Circulatory disorder (C) Neoplasia marker (D) No clinical significance (E) Nutritional deficiency
ANSWER: A: Cilia Rationale: Ductuli efferent are intratesticular ducts that transport sperm from the rete testis to the caput epididymis. These ducts (10 to 20) are lined by a simple epithelium composed of two populations of cells: (1) cuboidal cells with microvilli for water absorption and (2) tall columnar cells with cilia for generating fluid movement. This arrangement of tall ciliated cells and short absorptive cells gives the efferent ductules a distinctive scalloped appearance when examined on cross-section. Most of the fluid secreted by the seminiferous epithelium is absorbed by this epithelium. Lamellar bodies (choice E) are lipid-rich granules found in pneumocytes and keratinocytes. None of the other ultrastructural features characterize epithelial cells of the ductuli efferentes.
Which of the following cytologic features characterizes the epithelial cells that line the efferent ductules of the testes? (A) Cilia (B) Dense, membrane-bound secretory granules (C) Glycogen-rich vacuoles (D) Intracellular lipid droplets (E) Lamellar bodies
ANSWER: D: Spermatogonia Rationale: The blood-testis barrier separates premeiotic germ cells from post-meiotic germ cells. Spermatogonial stem cells and spermatogonia are adherent to the basement membrane (tunica propria) of the seminiferous epithelium and are located in the basal compartment of the seminiferous tubule. Early spermatocytes must move past Sertoli tight junctions to enter the adluminal compartment. It is believed that Sertoli cells control this process by forming new tight junctions below primary spermatocytes and simultaneously degrading tight junctions above these cells. The other germ cells listed are located within the adluminal compartment of the seminiferous epithelium.
Which of the following germ cells would be observed within the basal compartment of the seminiferous epithelium? (A) Primary spermatocytes (B) Secondary spermatocytes (C) Spermatids (D) Spermatogonia (E) Spermatozoa
ANSWER: B: Prostate gland Rationale: During embryonic development, the urorectal septum grows and divides the primitive hindgut (cloaca) into a urogenital sinus and a rectum. The primitive hindgut and its derivatives are lined by embryonic endoderm. The urogenital sinus is further divided into three parts: the cranial (vesicle) portion forms the urinary bladder; the middle (pelvic) portion forms the urethra and prostate in males and the entire urethra in females; and the caudal (phallic) part grows toward the genital tubercle to form the penis or clitoris. The other male reproductive organs are derived from mesoderm (mesenchyme) of the urogenital ridge.
Which of the following organs of the male reproductive system is derived from embryonic endoderm of the urogenital sinus? (A) Epididymis (B) Prostate gland (C) Seminal vesicles (D) Seminiferous tubules (E) Vas deferens
ANSWER: D: Opening of membrane Ca2+ channels Rationale: Following post testicular maturation in the epididymis, sperm must undergo capacitation in the female reproductive tract before they are competent to undergo fertilization. Capacitation results in hyperactivation of sperm motility and an increased ability of sperm to bind receptors on the zona pellucida. Biochemical changes associated with sperm capacitation include increased activity of adenylate cyclase, increased tyrosine phosphorylation, activation of membrane Ca2 + channels (correct answer), and other modifications of the sperm plasma membrane and glycocalyx. None of the other choices is associated with hyperactivation of sperm motility.
Which of the following signaling mechanisms plays an important role in mediating "hyperactivation" of sperm motility during capacitation in the female reproductive tract? (A) Activation of intracellular guanylate cyclase (B) Activation of membrane Na/K ATPase (C) Mitochondrial membrane permeability transition (D) Opening of membrane Ca2 + channels (E) Prostaglandin receptor binding
ANSWER: C: Intercellular bridges Rationale: Spermatogenesis is characterized by clonal cell divisions within the seminiferous epithelium. Daughter cells arising from a single type A (dark) spermatogonial stem cell remain intimately connected to one another through intercellular bridges. These open connections are the result of incomplete cytokinesis during mitotic and meiotic cell divisions. Intercellular bridges permit haploid nuclei to share molecular resources, including RNA, proteins, and various signaling molecules. Sharing resources helps coordinate the progression of germ cells through the stages of spermatogenesis and spermiogenesis. Intercellular bridges are lost prior to the release of spermatozoa into the lumen of the seminiferous tubule.
Which of the following structures helps regulate germ cell differentiation by ensuring free diffusion of signaling molecules, RNA, and proteins between daughter spermatocytes and spermatids within the seminiferous epithelium? (A) Desmosomes (B) Gap junctions (C) Intercellular bridges (D) Nuclear pores (E) Tight junctions
ANSWER: B: Sertoli cells Rationale: FSH and LH are glycoprotein hormones secreted by the anterior lobe of the pituitary gland. They regulate the ovarian cycle in females and spermatogenesis in males. Sertoli cells have cell surface receptors for both FSH and testosterone and serve as the primary regulators of spermatogenesis. Interstitial cells of Leydig (choice A) have receptors for LH and produce testosterone. Germ cells (choices C, D, and E) do not express cell surface receptors for FSH and LH.
You are asked to discuss the hormonal regulation of testicular function during a clinical conference. Which of the following cells in the postpubertal testes have receptors for both FSH and testosterone and serve as the primary regulators of spermatogenesis? (A) Leydig cells (B) Sertoli cells (C) Spermatids (D) Spermatocytes (E) Spermatogonia
ANSWER: E: Yolk sac endoderm Rationale: (PGCs) are set aside from somatic cells during the early development. PGCs leave the epiblast during gastrulation and move in a caudal direction through the primitive streak. It has been possible to trace the origin and migration of PGCs because they express high levels of cell surface alkaline phosphatase. Using enzyme histochemistry, PGCs are identified in the yolk sac endoderm near the origin of the allantois during the 4th week of development. With subsequent folding of the embryo, PGCs are moved with the primitive gut into the intraembryonic coelom. These large, amoeboid cells migrate along the dorsal mesentery of the hindgut to reach the gonadal ridge during the 5th week of development. The inner cell mass of the blastocyst (choice A) represents a small cluster of embryonic stem cells that give rise to germ line and somatic cells of the embryo; however, PGCs cannot be identified at this stage. Lateral plate mesoderm (choice B) gives rise to the appendicular skeleton and connective tissue of the lateral body wall. Paraxial mesoderm (choice C) givesrise to the axial skeleton, skeletal muscle, and der- mis. Trophectoderm of the blastocyst (choice D) is anextraembryonic epithelium that establishes contact with the maternal endometrium during implantation.
You are asked to give a lecture on the developmental biology of the male reproductive system. During early development, primordial germ cells (PGCs) can be unambiguously identified first in which of the following locations? (A) Inner cell mass (B) Lateral plate mesoderm (C) Paraxial mesoderm (D) Trophectoderm (E) Yolk sac endoderm
ANSWER: A: Dilation of helicine arteries Rationale: Penile erection is a complex neurophysiological process in which erectile masses of the penis become engorged with blood. In brief, parasympathetic stimulation initiates erection by causing relaxation of trabecular smooth muscle cells surrounding the helicine arteries. Dilation of these arteries causes the cavernous sinuses to fill with blood. Expansion of erectile masses leads to compression of veins and venules against the (nondistensible) tunica albuginea, resulting in rigidity of the penis. Acetylcholine and nitric oxide stimulate relaxation of smooth muscle during erection. Sympathetic stimulation terminates erection by causing contraction of trabecular smooth muscle cells. Erectile dysfunction represents an inability to achieve and maintain an erection that is sufficient for normal intercourse. Cardiovascular disease and diabetes are linked to the pathogenesis of erectile dysfunction.
A 64-year-old man with a history of hyperlipidemia and ischemic heart disease asks questions about treatment options for erectile dysfunction. Which of the following best explains the normal physiological mechanism for penile erection? (A) Dilation of helicine arteries (B) Dilation of spiral arteries (C) Vasoconstriction of helicine arteries (D) Vasoconstriction of spiral arteries (E) Vasoconstriction of trabecular arteries
ANSWER: B: Seminal vesicle Rationale: Examination of this image reveals a highly folded secretory epithelium, surrounded by a thin layer of smooth muscle. None of the other male reproductive organs exhibit this distinctive morphology. The paired seminal vesicles are tortuous tubes, measuring approximately 15 cm in length. They arise as outgrowths from the mesonephric ducts during embryonic development. Bladder cancer accounts for 3% to 5% of all cancer-related deaths. Urothelial (transitional) cell carcinoma of the bladder typically manifests as sudden hematuria and, less frequently, manifests as dysuria.
A 65-year-old man with a history of bladder cancer develops multiple organ system failure and expires. The patient's urogenital organs are examined at autopsy for evidence of malignant disease. Identify the normal male reproductive organ shown in the image. (A) Prostate gland (B) Seminal vesicle (C) Seminiferous tubule (D) Urinary bladder (E) Vas deferens
ANSWER: D: Leydig cells Rationale: Leydig cell tumors are rare gonadal stromal/sex cord tumors composed of cells resembling interstitial (Leydig) cells of the testis. They can be hormonally active and secrete androgens, estrogens, or both. The androgenic effects of testicular Leydig cell tumors in pre-pubertal boys lead to precocious physical and sexual development. By contrast, feminization and gynecomastia are observed insome adults with this tumor. The other choices do not induce precocious puberty.
A 9-year-old boy is brought to the physician by his parents who are concerned about the onset of puberty in their child. Physical examination reveals facial hair and enlargement of external male genitalia. Laboratory studies show elevated serum levels of testosterone. This patient may have a testosterone-producing tumor derived from which of the following endocrine cells? (A) Chief cells (B) Follicular cells (C) Granulosa cells (D) Leydig cells (E) Sertoli cells
ANSWER: C: Middle piece Rationale: The human spermatozoan has a flat, pointed head and a long tail (flagellum). The tail is divided into a short neck, middle piece, principal piece, and end piece. The middle piece of the spermatozoan contains mitochondria arranged in a helical fashion around outer dense fibers of the axonemal complex. These mitochondria provide ATP to generate whip-like motion of the flagellum (sperm motility). Of clinical significance, is the observation that sperm-associated mitochondria do not survive fertilization. As a result, the mitochondria of the embryo and adult are derived from the ovum at fertilization (i.e., maternal mitochondrial inheritance).
A couple complains that they have been unable to conceive a child for the past 2 years. The man's sperm count is within the normal reference range. Electron microscopic examination of a sperm sample reveals a normal distribution of mitochondria. These intracellular organelles are located in which of the following regions of the spermatozoan? (A) Acrosome (B) End piece (C) Middle piece (D) Neck (E) Principal piece
ANSWER: A: Corpus cavernosum Rationale: The erectile tissues of the penis include paired corpora cavernosa and a ventral corpus spongiosum (choice B). These cavernous spaces become engorged with blood in response to parasympathetic stimulation during penile erection. Tunica albuginea (choice C) is a dense fibroelastic layer that holds the cylindrical erectile masses together. This structure is visible in the image as a reddish band surrounding the paired corpora cavernosa. Tunica vaginalis (choice D) and tunica vascularis (choice E) are investing layers of the testes.
A cross-section of the penis is examined in the histology laboratory (shown in the image). Identify the structure indicated by the arrow. (A) Corpus cavernosum (B) Corpus spongiosum (C) Tunica albuginea (D) Tunica vaginalis (E) Tunica vascularis
ANSWER: B: Leydig cells Rationale: The SRY gene carried on the Y chromosome initiates gonadal sex determination, in part, by inducing the differentiation of Sertoli cells and Leydig cells in the embryonic testes. Testosterone secreted by interstitial cells of Leydig stimulates the growth and differentiation of male excurrent genital ducts, as well as morphogenesis of male external genitalia. Follicular cells of the ovary (choice A) secrete estrogen when activated by FSH after puberty. None of the other cells secrete androgens.
During a research seminar, you are asked to discuss signaling molecules that control the development of the male reproductive system. Which of the following cells in the developing human embryo secrete a steroid hormone that stimulates the growth and differentiation of excurrent genital ducts, including the epididymis and vas deferens? (A) Follicular cells (B) Leydig cells (C) Primordial germ cells (D) Sertoli cells (E) Spermatogonia
ANSWER: B: Patch-like Rationale: Spermatogenesis is the process of generating sperm from a self-renewingpopulation of stem cells. Spermatogenesis begins at puberty and continues throughout life. Spermatogonial stem cells continuously generate spermatogonia that enter meiosis to form spermatocytes (primary andsecondary), spermatids (early and late), and sperm. Extensive remodeling of spermatids to yield sperm istermed spermiogenesis. The process whereby late spermatids are released into the lumen of the seminiferous tubule is termed spermiation. The stages of spermatogenesis are not randomly distributed throughout the seminiferous tubules of the testes. Rather, groups of cells at the same stage of differentiation appear together.This grouping reflects the clonal nature of spermatogenesis, with daughter cells connected as a syncytium. In many species, spermatogenesis occurs in cycles that appear as "waves" running along the seminiferoustubules (choice E). However, recent studies indicate that spermatogenesis in humans is patch-like. Stages of spermatogenesis in humans do not extend around the circumference of the tubule, nor do they proceed sequentially along the seminiferous tubule. None of the other choices describe cycles of spermatogenesis in humans.
Beginning at puberty, under the influence of pituitary FSH and LH, the testes initiate spermatogenesis and produce sperm. Which of the following best describes the topological organization of cycles of spermatogenesis that occur in the seminiferous tubules after puberty? (A) Lobular (B) Patch-like (C) Random (D) Uniform (E) Wave-like
ANSWER: E: Prostatic urethra Rationale: The prostate is the largest of the male accessory glands. It is located in the pelvis, below the urinary bladder. The prostate gland is divided into three zones: central, transitional, and peripheral. The transitional zone surrounds the prostatic urethra, and the central zone surrounds the paired ejaculatory ducts. Nodular hyperplasia of the prostate is a common disorder characterized clinically by enlargement of the gland and obstruction to the flow of urine through the bladder outlet, and pathologically by the proliferation of glands and stroma. Nodular prostatic hyperplasia results in the retention of urine in the bladder and predisposes to recurrent urinary tract infections. Enlargement of the prostate does not affect the other structures listed.
Digital rectal examination of a 68-year-old man reveals an enlarged prostate gland. Serum levels of prostate-specific antigen (PSA) are mildly elevated (6.8 ng/mL, normal reference range = 0 to 4 ng/mL). Enlargement of the transitional zone of the prostate in this patient would primarily affect which of the following urogenital structures? (A) Anal canal (B) Duct of seminal vesicles (C) Ductus deferens (D) Penile urethra (E) Prostatic urethra
ANSWER: C: Fructose Rationale: The accessory glands of the male reproductive tract include paired seminal vesicles, the prostate gland, and several bulbourethral glands. These organs produce secretions that mix with sperm to form semen during ejaculation. Most (70%) of the fluid in semen is contributed by the seminal vesicles. Evidence of this viscous fluid is evident in the image. This foamy liquid contains an abundance of amino acids, simple sugars, prostaglandins (arachidonic acid derivatives), enzymes, and other proteins. Fructose is a six-carbon monosaccharide that serves as the principal metabolic substrate for sperm motility. Pyruvic acid (choice E) is a product of glycolysis and an energy source for the Krebs cycle; however, this three-carbon ketone is not secreted by the seminal vesicles. None of the other choices provide a significant source of energy for oxidative phosphorylation in sperm.
Microscopic examination of a seminal vesicle from a different patient shows evidence of a foamy, secretory material with the lumen of the gland (asterisk, shown in the image). Which of the following secretory products of the seminal vesicle provides the principal metabolic substrate for sperm in semen? (A) Amino acids (B) Ascorbic acid (C) Fructose (D) Prostaglandins (E) Pyruvic acid
ANSWER: D: Fibromuscular stroma Rationale: The prostate gland contains 30 to 50 branched tubuloalveolar glands, surrounded by a fibromuscular stroma. The ducts of these glands drain to the prostatic urethra. The stroma is composed of dense, irregular connective tissue, with an abundance of smooth muscle fibers that help to expel fluid during ejaculation. Epithelial cells of the prostate gland secrete an alkaline fluid thatcombines with sperm and secretions of the seminal vesicles to form semen. Secretions of the prostate glandcontain prostatic acid phosphatase and proteolytic enzymes that are important for the process of fertilization.None of the other choices are histologic features of the prostate gland.
Microscopic examination of the prostate gland from a different patient is shown in the image. Which of the following is a distinctive histologic feature of this male reproductive organ? (A) Apical membrane stereocilia (B) Colloid-filled follicles (C) Epithelial cords and sinusoidal capillaries (D) Fibromuscular stroma (E) Stratified cuboidal epithelium
ANSWER: B: Primary spermatocytes Rationale: The seminiferous epithelium is filled with meiotic and postmeiotic cells in the process of making sperm. Some of the stages in spermatogenesis last longer than others. For example, primary spermatocytes in humans are arrested in prophase of meiosis I for about 22 days. This pause in the cycle of spermatogenesis provides time for homologous chromosomes to undergo crossing-over without DNA insertions or deletions. By contrast, secondary spermatocytes are very short-lived cells that rapidly complete the second meiotic division (meiosis II) to form haploid spermatids. Spermatogonial stemcells are very rare cells that have only recently been identified and cultured. Spermatogonia and Sertoli cells are less abundant than are meiotic cells in seminiferous tubules.
On average, when examined by light microscopy, of the following testicular cells is most abundantly represented in the seminiferous epithelium of an adult? (A) Leydig cells (B) Primary spermatocytes (C) Secondary spermatocytes (D) Sertoli cells (E) Spermatogonia
ANSWER: A: Cremaster muscle Rationale: This image shows a cross-section through the spermatic cord. The spermatic cord carries nerves and blood/lymph vessels from the posterior abdominal wall to the scrotum, and it carries the vas deferens from the scrotum to the prostate gland. The arrows on this image identify the cremaster muscle. These skeletal muscle fibers cover the spermatic cord. They represent a portion of the internal oblique muscle that extends through the inguinal canal. The cremasteric reflex serves to raise the testicles, toward the abdominal wall, in response to low temperature to safeguard spermatogenesis. Dartosfascia (choice B) is the superficial fascia of the penis and scrotum. The aponeurosis of the external oblique muscle (choice C) forms the anterior wall of the inguinal canal. The pampiniform venous plexus (choice D, shown in the image) consists of anastomosing branches of the spermatic vein. This plexus serves as a heatex changer to lower the temperature of arterial blood entering the testes. Paired testicular arteries (choice E) arise from the abdominal aorta.
The organ that is derived from embryonic endoderm of the urogenital sinus is examined at low magnification. Identify the structure indicated by the arrows. (A) Cremaster muscle (B) Dartos fascia (C) External oblique muscle (D) Pampiniform venous plexus (E) Testicular artery
ANSWER: E: Stereocilia Rationale: This low-magnification image shows a cross-section through the epididymis. The epididymides are highly convoluted, 4-m ducts, located along the superior and posterior aspect of the testes. The epididymis can be divided into three segments (proximal to distal): caput, corpus, and cauda. During transit through the epididymis, sperm gain the ability to undergo capacitation and fertilization. This process is referred to as "post testicular sperm maturation." Epithelial cells lining the epididymis are notable for the presence of nonmotile stereocilia. These apical membrane structures are actually long microvilli that contain actin filament cores (not tubulin, as would be expected in true cilia). Stereocilia are thought to be involved in fluid/electrolyte transport. None of the other ultrastructural features characterize the epithelial cells of the epididymis.
The reproductive organs of a 55-year-old man are examined at autopsy (shown in the image at low magnification). Which of the following cytologic features characterizes the epithelial cells that line this portion of the excurrent duct system? (A) Basal glycogen-rich vacuoles (B) Dense, membrane-bound secretory granules (C) Intracellular lipid droplets (D) Perinuclear halos (E) Stereocilia
ANSWER: D: Rete testis Rationale: The seminiferous tubules terminate as short stubs (tubuli recti, choice E) that empty into an interconnected labyrinth of channels referred to as the rete testis. These anastomosing channels are embedded in dense connective tissue that is continuous with that of the tunica albuginea. The rete testis is lined by a simple cuboidal epithelium. It provides a conduit for sperm and fluid to leave the testis for the epididymis, by way of efferent ductules (ductuli efferentes, choice B). The efferent ductules of the testis have an unusual scalloped appearance when examined on cross-section. None of the other ducts are surrounded by dense connective tissue within the mediastinum of the testis.
The specimen is examined at higher magnification (shown in the image). Identify these ducts that are lined by a simple cuboidal epithelium. (A) Epididymis (B) Ductuli efferentes (C) Ductus deferens (D) Rete testis (E) Tubuli recti
ANSWER: A: Endothelial cells Rationale: This image shows a portion of the corpus spongiosum adjacent to the spongy urethra. The cavernous spaces are components of the vascular system and lined by vascular endothelial cells. The spongy urethra is, for the most part, lined by a pseudostratified epithelium; however, the epithelium in this specimen appears stratified. Mesothelial cells (choice B) are simple squamous epithelial cells that line the body cavities (e.g., pericardium and peritoneum). Myoepithelial cells (choice C) are contractile cells that surround excretory ducts. Myofibroblasts (choice D) are contractile cells that differentiate from mesenchymal stem cells within granulation tissue to promote wound healing by primary intention. Smooth muscle cells (choice E) do not line vascular channels.
The tissue specimen is examined at higher magnification (shown in the image). Which of the following types of cells lines the cavernous sinuses in this erectile tissue? (A) Endothelial cells (B) Mesothelial cells (C) Myoepithelial cells (D) Myofibroblasts (E) Smooth muscle cells
ANSWER: E: Smooth endoplasmic reticulum Rationale: Enzymes involved in the synthesis of steroid hormones such as testosterone and estrogen are associated with membranes of the smooth endoplasmic reticulum. Elaborate smooth endoplasmic reticula are a characteristic ultrastructural finding in steroid-secreting cells. None of the other organelles organizes enzymes involved in testosterone biosynthesis.
The tumor is removed and examined by light microscopy in the pathology department. Sections of the surgical specimen are stained with an antibody that binds to a key enzyme in the testosterone biosynthetic pathway. This enzyme is located in which of the following cellular organelles? (A) Golgi apparatus (B) Peroxisomes (C) Plasma membrane (D) Rough endoplasmic reticulum (E) Smooth endoplasmic reticulum
ANSWER: D: Organization and differentiation of gonadal cords Rationale: During the 5th week of development, the indifferent gonads form finger-like, epithelial cords that project into the underlying mesenchyme. Male and female PGCs arriving in the indifferent gonad are incorporated into these primitive sex cords. In male embryos, testis-determining factor (TDF), encoded by the SRY gene, stimulates primitive sex cords to extend deeper into the medulla of the gonad. TDF also stimulates the differentiation of Sertolicells and Leydig cells, which secrete müllerian-inhibiting factor and testosterone, respectively. The differentiation of Sertoli cells under the influence of TDF appears to be a critical step in male gonadal sex determination. Female PGCs arrest in prophase of meiosis I (choice A). Testosterone and dihydrotestosterone regulate the development of the male external genitalia (choice B), as well as differentiation of the mesonephric tubules and ducts (choice C). Regression and loss of the uterus and the uterine tubes (choice E) are regulated by müllerian-inhibiting factor.
You are conducting research on mechanisms on gonadal sex determination. What is the principal effect of testis-determining factor (TDF) on the development of the male reproductive system? (A) Arrest of PGCs in prophase of meiosis I (B) Development of male external genitalia (C) Differentiation of mesonephric tubules and ducts (D) Organization and differentiation of gonadal cords (E) Regression and loss of the uterus and uterine tubes
ANSWER: C: Gap junctions Rationale: Junctional specializations of Sertoli cells in the seminiferous epithelium include tight junctions, gap junctions, desmosomes, and hemidesmosomes. Tight junctions create a permeability barrier between basal and adluminal compartments of the seminiferous tubules. Numerous gap junctions are also present between adjacent Sertoli cells. These junctions provide ionic coupling in the seminiferous epithelium and help coordinate the cycle of spermatogenesis. Hemidesmosomes connect the basal membranes of Sertoli cells to their underlying basal lamina. None of the other choices mediate signaling between adjacent Sertoli cells.
You are conducting research on the role of Sertoli cells in spermatogenesis. Which of the following cellular components permits signaling between adjacent Sertoli cells and helps coordinate the cycle of spermatogenesis within the seminiferous epithelium? (A) Actin filament bundles (B) Endosomes (C) Gap junctions (D) Hemidesmosomes (E) Phagolysosomes
ANSWER: A: Acrosome Rationale: During spermiogenesis, small vesicles of the Golgi apparatus coalesce to form a large membrane-bound vesicle adjacent to the nucleus. In mature spermatozoa, this acrosomal cap covers the anterior two-thirds of the nucleus. It contains a variety of glycoprotein enzymes, including hyaluronidase, neuraminidase, acid phosphatase, and protease (acrosin). Binding of spermatozoa to receptors on the zona pellucida triggers the acrosome reaction. During this reaction, the sperm plasma membrane fuses with the membrane of the acrosomal cap, thereby liberating acrosomal enzymes. These hydrolytic enzymes allow sperm to penetrate the corona radiata and zona pellucida and reach the plasma membrane of the secondary oocyte during fertilization. None of the other choices describe the location of the acrosomal cap in human sperm.
You are involved in a research project to investigate mechanisms of fertilization. Hydrolytic enzymes that are necessary for sperm penetration of the zona pellucida are packaged in which of the following regions of the spermatozoan? (A) Acrosome (B) End piece (C) Middle piece (D) Neck (E) Principal piece
ANSWER: E: Residual bodies Rationale: The image shows late spermatids at the time of their release from the seminiferous epithelium. Acrosomal caps and sperm flagella are visible in this section. Prior to their release, late spermatids break intercellular bridges and shed residual cytoplasm. These residual bodies are internalized by Sertoli cells and degraded within phagolysosomes. Once this process has been completed, spermatozoa are released from Sertoli cells into the lumen of the seminiferous tubule. Contractions of myoid cells in the peritubular connective tissue help to propel the male gametes on their journey through the excurrent duct system. None of the other cellular structures are shed from late spermatids during spermiogenesis.
You are involved in research to identify pharmacologic compounds that inhibit the release of sperm into the lumen of the seminiferous tubule. This process of spermiation is revealed in a thin section of the hamstertestis (shown in the image). Which of the following structures is removed from late spermatids prior to the release of sperm into the lumen of the seminiferous tubules? (A) Acrosomal caps (B) Fibrous sheaths (C) Nuclear membranes (D) Polar bodies (E) Residual bodies
ANSWER: D: Sertoli cells Rationale: The blood-testis barrier separates meiotic and post meiotic cells in the seminiferous epithelium from antibodies, pathogens, and toxins in the blood. This permeability barrier is established by the presence of tight junctions (zonula occludens) between adjacent Sertoli cells. Meiotic and haploid germ cells are located within the adluminal compartment of the seminiferous epithelium. This immunologically privileged environment is believed to protect developing germ cells from recognition and destruction by B and T lymphocytes that might otherwise become activated by "sperm-specific antigens." The blood-testis barrier also serves to concentrate secretions of Sertoli cells (e.g., testosterone and dihydrotestosterone) toward the lumen of the tubule. None of the other cells contribute to the blood-testis barrier.
You attend a research seminar on the pathobiology of testicular cancer. Questions are raised during the talk regarding the blood-testis barrier. You explain that the seminiferous epithelium is divided into basal and adluminal compartments as a result of tight junctions between which of the following testicular cells? (A) Leydig cells (B) Myoid cells (C) Primary spermatocytes (D) Sertoli cells (E) Spermatids